14 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 63, 



shifting to a vertical position and consequently becoming closely ap- 

 pressed to that protuberance. If one attempts a restoration of the 

 back of the skull by following the curvature suggested by that 

 fragment of the supraoccipital which is preserved, then the area be- 

 tween the lambdoidal crests was higher than wide, but otherwise 

 bore considerable resemblance to Inia. 



Lateral view. — A narrow rostrum equaling five times the length 

 of the cranium, a large supraorbital process forming a high crest 

 above the orbit, a thickened zygomatic process of the squamosal, and 

 the absence of an elevated vertex, all contribute to the formation of 

 a skull (pi. 2) that is unlike either Lipotes., Inia^ or Platanista. As 

 in other long-beaked dolphins, the rostrum is formed mainly by the 

 closely joined maxillae and premaxillae, these elements being sup- 

 ported internally by the anterior extension of the vomer. More than 

 half of the lateral aspect of the rostrum is formed by the maxilla. 

 The premaxilla is shallower than the maxilla, decreasing in height 

 anteriorly and near the tip of the rostrum is barely visible from a 

 side view. The axis of the rostrum is approximately straight. In 

 this skull and in that of Lipotes the rostrum is noticeably broader 

 than deep; this feature is more evident in the former than in the 

 latter. On the other hand the rostrum of the skull of Inia is rela- 

 tively deeper throughout its length and appears to be bent down- 

 ward. 



In this specimen the lambdoidal crests were apparently the highest 

 points of the dorsal profile ; in front of these the maxillae slope for- 

 ward to the rostrum. The skull as a whole is very slender, and the 

 height at the vertex is proportionately low in comparison with that 

 of the base of the rostrum. The alveolar gutter is visible throughout 

 its length from a side view and terminates 118 mm. in advance of the 

 maxillary notch. The temporal fossa as restored is relatively small 

 and equals about twice the length of the orbit. 



Above the orbit the supraorbital process of the frontal is bent 

 abruptly upward and forms a vertical crest. The maxilla also bends 

 upward and sheathes the internal face of this crest ; the external mar- 

 gin of the maxilla bends over and is closely appressed to the anterior 

 and dorsal faces. The greatest vertical depth of the left supraorbital 

 process of the frontal is 81 mm., and the greatest length is 105 mm. 

 The crestlike portion of the supraorbital process is reduced to a mere 

 vestige in Lipotes^ Inia, and Platanista. 



The external face of the supraorbital process slopes obliquely up- 

 ward and inward. It is " fan-shaped " in outline, the anterior and 

 dorsal margins being evenly rounded, while the posterior margin 

 is nearly straight, and the ventral margin is emarginate. Pos- 

 teriorly, the supraorbital process is drawn out into a narrow post- 

 orbital projection which slopes downward ; it thus comes in contact 



